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Tuesday, May 23, 2017

Variation among pad foundation, strip foundation and raft foundation

Shallow foundation is generally described as foundation that
contains founding level below 3m from ground surface. Alternatively, when the
breadth of the lower most part of the foundation is more than the depth of the
lower most part of the foundation from the uppermost of the soil, i.e. Ground
Level then it is defined as a Shallow Foundation. It transmits building loads
to the earth adjacent to the surface. Shallow foundations comprise of spread
footing foundations, mat-slab foundations, slab-on-grade foundations, pad
foundations, rubble trench foundations and earthbag foundations.

Pad foundation stands
for the foundation that is specifically developed for retaining concentrated
loads out of a single point load like structural columns. Pad foundations are specifically
designed to provide support to individual or multiple columns, scattering the
load to the ground underneath. They are usually square or rectangular in plan,
the plan area is defined by the allowable bearing pressure of the soil. The
shape in plan will be determined by the arrangement of the columns and the load
will be transmitted into the soil.

The thickness of the slab should be adequate to make sure
that distribution of the load is perfect. The top of the pad should have been
sloping (i.e. the pad is denser in the centre as compared to it is at the
edge). It provides a cost-effective solution, though there are construction
issues which are associated with casting the slope.

Strip foundation is
utilized to provide support to a line of loads like load-bearing walls. As for
example, closely-placed columns deliver the imperfect application of pad
foundation and strip foundation may be a good choice.

Raft foundation comprises of a concrete slab which
expands over the entire loaded area in order that loads from whole structure
are expanded over a broader area that results in minimizing of the stress of
foundation soils. Besides, raft foundation is useful for resisting differential
settlement.